The present disclosure generally relates to seismic data acquisition and processing, and more particularly to real-time infill in marine seismic surveys using an independent seismic source.
Petrochemical products such as oil and gas are ubiquitous in society and can be found in everything from gasoline to children's toys. Because of this, the demand for oil and gas remains high. In order to meet this high demand, it is important to locate oil and gas reserves in the Earth. Scientists and engineers conduct “surveys” utilizing, among other things, seismic and other wave exploration techniques to find oil and gas reservoirs within the Earth. These seismic exploration techniques often include emitting seismic energy into the Earth with a seismic energy source (e.g., dynamite, air guns, vibrators, etc.), and monitoring the Earth's response to the seismic source with one or more receivers in order to create an image of the subsurface of the Earth.
Certain types of marine seismic surveys involve towing one or more streamer cables with a plurality of receivers behind an acquisition vessel along pre-plotted sail lines. Each receiver includes, for example, a pressure sensor, a particle motion sensor, or both a pressure sensor and a particle motion sensor in proximity to one another. The pressure sensor may be, for example, a hydrophone that records scalar pressure measurements of a seismic wavefield. The particle motion sensor may be, for example, a three-component geophone or accelerometer that records vectorial velocity measurements of the seismic wavefield. By observing the reflected seismic wavefield detected by the receiver(s) during the survey, the geophysical data pertaining to reflected signals may be acquired and these signals may be used to form an image indicating the composition of the Earth near the survey location.
During the course of such a marine seismic survey, many factors can affect the seismic data that is acquired. For example, ocean currents or other environmental factors can cause the acquisition vessel and/or the streamer cables to deviate from their pre-plotted and intended courses, which may lead to gaps or holes in the coverage of the acquired seismic data. Also, some sources or receivers may malfunction. Also, different events may cause data that is acquired to be low quality or noisy. These factors, as well as other factors, may impact the quality and/or quantity of the seismic data that is acquired for certain subsurface regions.
In conventional marine seismic streamer surveys, the acquisition vessel and streamer cables typically complete many sail lines to acquire seismic data over a relatively large area of the subsurface. Following the completion of a number of adjacent sail lines of that initial, primary seismic data acquisition survey, the acquired seismic data may be analyzed (e.g., the coverage) to determine whether any “infill” seismic data needs to be acquired. Infill seismic data may need to be acquired if, for example, the coverage of a certain area is less than a predetermined threshold (e.g., if certain common midpoint bins are less than a certain percentage full). In order to acquire such infill seismic data, the one or more streamer cables with a plurality of receivers are again towed behind the acquisition vessel over appropriate subsurface regions in an attempt to infill the data. Such infill operations, like the primary acquisition, can be quite costly, especially because the acquisition vessel typically has left the area before the determination is made that infill seismic data is needed. In addition, infilling seismic data can delay data processing and analysis, and, depending on weather and other conditions during the infill operation, the desired seismic data may not even be acquired.